1. Field of the Invention
The present invention relates to an apparatus for lighting a High-Intensity Discharge (HID) lamp, such as a high pressure mercury lamp or a metal halide lamp. Particularly, the present invention relates to a discharge lamp lighting apparatus which can control in detail lighting processes of a high pressure discharge lamp depending upon its individual characteristics and also upon its operating state.
2. Description of the Related Art
Since the HID lamp is in general lighted through various phases of (1) occurrence of Townsent current, (2) occurrence of glow discharge, (3) growth of arc discharge, and (4) stable arc discharge, very complicated lighting process controls are necessary for ensuring stable lighting. In a conventional discharge lamp lighting apparatus, most of such the complicated process controls are executed by using various timers and analog circuits (described in, for example, EP-A1-0 536 535). Thus, the conventional apparatus has to be constituted by a large number of analog components and therefore has complicated structure and large size, resulting its manufacturing cost to extremely increase.
Furthermore, according to such the analog type lighting control apparatus, detail and adaptive lighting control of the lamp depending upon its individual characteristics and also upon its operating state cannot be expected.
For the lighting apparatus, since there are many kinds of discharge lamps having different lamp characteristics, a general purpose lighting apparatus, not specially designed lighting apparatus is desired.
For a discharge lamp lighting apparatus, furthermore, detail control to secure safety operation of the discharge lamp and protection of the discharge lamp are required. For example, safety control for preventing excess ignition pulses against the lamp at starting from occurring will be necessary, and also protection of the discharge lamp by stopping the operation of the lighting control apparatus when its internal circuit such as an inverter circuit malfunctions will be necessary.